Transmit-receive tube



y 1, 1960 J. R. FALLON, JR 2,939,043

TRANSMIT-RECEIVE TUBE Filed Oct. 17, 1957 2 Sheets-Sheet 1 IN VEN TOR.

JOSEPH 1?. F144 L O/V J19.

fiaf/zw r' ATTORNEY May 31, 1960 J. R. FALLON, JR

TRANSMIT-RECEIVE TUBE 2 Sheets-Sheet 2 Filed Oct. 17, 1957 FIG. 4

INVENTOR. JOSEPH 1?. F944 01v dz BY w,

ATTORNEY United States Patent The present invention relates to gaseous discharge switching devices of the transmit-receive type and more particularly to improved tuning apparatus forsuch de-.

Vices. I I j Conventional transmit-receive tube construction comprises both inductive and capacitive resonant elements disposed within a section of selected waveguide forming the tube envelope. Such devices are evacuated and filled with ionizable atmospheres at reduced pressures selected for optimum characteristics at the microwave frequencies desired. "Detailed'descriptions of the prior art devices will be found inthe text Microwave Duplexers by L. D. Smullin and C; G. Montgomery, McGraw-Hill Book Co, New York, 1948 and U. S, Patents 2,608,207, issued June 1,1954 to H. C. Booth and 2,524,268, issued Octoher 3, 1950 to H. J. McCarthy.

The tube envelope structure generally comprises a section of rectangular waveguide having parallel broad walls and narrow side walls. At microwave frequencies in the region above 3000 megacycles tube envelope dimensions remain substantially unaltered by atmospheric pressure. In the lower region of the spectrum, however, where rectangular guide is employed relatively larger wall areas are exposed to atmospheric pressures, which has resulted in impairment of performance due to movement of the metallic walls. This causes detuning of the capacitive gap electrodes normally secured to these walls. According to conventional methods of fabrication the devices of the so-called broadband type are always factory tuned to the resonant frequency and the tuning members are then hermetically sealed to preserve the vacuum condition. Hence, it is impossible to adjust the tuning once the tube is completely fabricated and variations due to atmospheric pressure on the envelope are noted.

Accordingly, it is an object of the present invention to provide an improved tuning apparatus for transmit-receive switching devices.

Another object is to provide apparatus for tuning of a transmit-receive switching device after evacuation to facilitate adjustment for variations caused by atmospheric pressure on the evacuated envelope.

Other objects, features and advantages will be apparent after consideration of the following detailed specification and appended drawings, in which:

Fig, l is a perspective view of an embodiment of the invention;

Fig. 2 is a cross sectional view along the line H-II in Fig. 1;

Fig. 3 is an enlarged perspective view of the capacitive members of the illustrative device embodying the invention; and

Fig. 4 is an enlarged detailed cross sectional view of the tuning member of the invention.

Referring to Fig. l, a broadband microwave frequency transmit-receive switching tube 1 is illustrated comprising a section of rectangular waveguide 2 enclosed at the ends thereof by metallic plates 3 having dielectric windows 4 ice 5 defines a reentrant projection 6 forming a capacitive electrode member. oppositely disposed is a threaded tuning member 7 threadably engaging sleeve 8 secured to the top wall of waveguide 2. The internal end of memher 7 may be pointed to define conical electrode 9 which together. with opposite electrode 6 forms the discharge gap 10. 'The ignitor electrode structure 11 may be fabricated in accordance with aforementioned Patent No.

2,524,268 and is introduced in the capacitive-inductive resonant system positioned one-quarter wavelength away. Flanges 12 disposed at each of waveguide 2 provide means for mounting of the tube in a waveguide system. Tubes of the character described are evacuated and may be filled with an inert gas at reduced pressures in the order of 5-30 millimeters of mercury depending on the desired'electrical characteristics.

According to prior art fabrication techniques the spacingbetween the electrode members is adjusted to the resonant frequency and then the outer projections of the tuning elements are soldered to the waveguide to provide a vacuum "tight seal. filled with the gas filling. Hence, after evacuation it is impossible to compensate for any deforming of'the waveguide envelope caused by atmospheric pressure on the outer walls.

In accordance with the teachings of the invention tuning member 7 is provided with structure which permits tuning after fabrication to compensate for atmospheric variations. Referring to Fig. 3 a tuning element 13 in the form of an elongated metallic rod is provided within an axial passageway in the main body member of the tuning apparatus 7. The control mechanism cooperating with the tuning element comprises a shaft 14 secured to the outer end of element 13 and a deformable metallic diaphragm 15 secured adjacent the base 16 of a cavity 17 in the outer end of member 7. The peripheral edges of the diaphragm 15 are secured to the cavity walls. Lower disc 18 fitted around shaft .14 provides a base support for spring 19 which in turn is biased against disc 20. Locking pin 21 extends through shaft 14 to secure disc 20 thereto. A plurality of pins 22 may be provided on either side of shaft 14 to center same as well as limit the upward movement of disc 20 to thereby prevent rupture of the diaphragm. One of the pins is shown with the ends thereof anchored to the Wall portion 23 defining cavity 17.

The inner walls of cavity 17 are threaded as at 24 with an t.p.i, thread being preferred. Plug 25 may then be threaded therein to engage shaft 14 and control projection of element 13 beyond the apex of electrode 9 to alter the tuning of the tube. Spring 19 urges disc 20 upwards which in turn maintains the shaft 14 in contact with plug 25. Hence, by simply rotating plug 25 pressure is applied or relaxed on the element 13.

In the fabrication of the switching device member 7 is positioned within sleeve 8 and the gap is tuned with the tip of element 13 projecting from the apex of electrode 9 a distance of approximately five to ten thousandths. The aforementioned dimension is an example of a particular embodiment in L-band and there will be variations The tube is then evacuated and depending on the frequency selected. The important factor is to extend the tuning element in the preliminary tuning in order that subsequent adjustments may be made by either retracting or further extending the element in the discharge gap. I a A retaining nut 26 is then secured against waveguide land a sealing material such as solder may be flowed in the region '27 to provide a vacuum seal. The tube is then evacuated and filled with an atmosphere containing an inert gas at reducedpressure with possibly a few millimeters of mercury of watervapor. i

After fabrication is completed any tuning adjustments may be made by varying the distance of element 13. Thevacuum condition is retained by the diaphragm which is flexible to respond to adjustments in'the projecting'dis: tance of the tuning element. There is thus disclosed a novel tuning apparatus permitting adjustments to compen sate for atmospheric pressureietfects prevalent in'prior art'transmi-t receive devices. T

What isclaimed isf 1. A transmit-receivegaseous discharge device comprising a length of waveguide having broad and narrow.

walls, plural resonant inductive iris and capacitive electrode members spaced. at' quarter wavelength intervals within said waveguide, at least one of said capacitive electrode members comprising a conical tipped body member secured to a broad wall and extending into said waveguide in register with and opposite to another electrode member,,said"'l5ody member defining an axial passageway tlierethrough andv a cavity at its outer end, a tuning element disposed within said passageway with its upper end terminating within said caivty, vacuum retaining means secured to said tuning element adjacent to said upper end with the peripheral edges thereof secured tothe cavity walls, screw actuated means positioned within said cavity to engage said tuning element and axially adjust the lower end to extend beyond said conical tip to thereby tune the device to a selected resonant frequency. a

2. A transmit-receive gaseous discharge device comprising a length of waveguide having broad and narrow walls, plural resonant inductive iris and capacitive electrode members spaced at quarter wavelength intervals within said waveguide, at least one of said capacitive electrode members comprising a' conical tipped screw secured to a broad'wall and extending'intosaid waveguide in register with and opposite to a conical tipped electrode member, saidscrew defining an axial passageway therethrough and an open-ended cavity at its outer end, a metallic rod element positioned within said passageway with its upper end terminating within said cavity, a'metallic convoluted diaphragm secured to said rod adjacent the base of said cavity with the peripheral edges thereof secured to the cavity walls, a rotatable threaded plug enclosing the open end of said cavity with its inner end communicating with said rod element and spring biasing means cooperating with said rod element androtatable plug to axially adjust said element to extend beyond said conical tip a distance determined by the selected resonant frequency of the device.

i References Cited in the file of this patent 1 I UNITED STATES PATENTS 

